The present invention relates to a household appliance utilizing water, in particular a washing machine, comprising a device for reducing the water hardness.
As it is known, certain household appliances like washing machines, in particular household dishwashers, are provided with a system, also known as a water decalcifier or softener, for reducing the water hardness; in particular, this system is provided for reducing the calcium and magnesium contents of the water used for washing purposes, which may inhibit the action of detergents and produce calcareous deposit; in fact, calcareous deposits are due to an excessive amount of calcium ions (Ca++) and magnesium ions (Mg++) contained in the water supplied by the main; in particular, calcium ions and magnesium ions are cations, i.e. ions with a positive electric charge.
To this purpose, the decalcifier provides for exchanging the calcium and magnesium ions of the water with sodium ions (Na+) contained in suitable decalcifying resins, which are in fact cationic, and therefore able to retain the positively charged calcium and magnesium ions. These resins, which are shaped like small balls, are placed in an appropriate container pertaining to the decalcifier, which is flushed through by the water supplied from the main.
Since the above resins exhaust their softening capability after a certain volume of treated water, they have to be regenerated by flushing them through with a water and sodium chloride solution (NaCl), commonly called brine; in this way, the calcium and magnesium ions deposited on the resins are replaced by the sodium ions of the brine, so that the resins are ready again for a new softening phase; in most instances, such a resins regenerating process occurs at each wash cycle performed by the machine. Therefore, water softening systems as above have to provide a salt container, which needs to be regularly topped up by the user, due to the consumption caused by the periodical resin regenerating processes.
In main line, it should be considered how the higher the water hardness degree is, the faster resins become exhausted, whereby a greater salt consumption is needed for resins regeneration; therefore, in other words, the salt consumption may be considered directly proportional to the hardness degree of the water used by the washing machine.
In order to reduce salt and water waste, some washing machines do not perform a resins regeneration phase at each wash cycle, but less frequently, typically after a predetermined amount of water have been softened; in other known solutions, the washing machine is equipped with water hardness sensors, which activate the regeneration phase only upon detecting that water hardness is not low enough, due to resins exhaustion; according to other solutions also utilizing water hardness sensors, the amount of brine supplied to the resins compartment is variable and proportional to the water hardness degree ascertained.
At any rate, the above softening technique has been well known and affirmed for several years in the field of household washing machines, based on its satisfactory reliability and convenience.
However, it is obvious that the above technique presumes a periodic maintenance or operation to the system by the user, which consists in topping up the salt in the relevant container; it is also clear that, whenever salt is not topped up and the resins cannot be regenerated, the system will not perform wash water decalcification as required.
To this purpose it will also be appreciated that the user should be promptly warned about a likely lack of salt in the relevant container; to this purpose, therefore, the washing machine should have appropriate sensing means indicating salt availability, usually based on the use of floats and relevant signalling means, such as a warning light. However, these sensing means are subject to failure or clogging, so that the salt container may remain erroneously empty, with an ensuing wrong and useless operation of the decalcifying system.
The document U.S. Pat. No. 4,645,595 discloses a washing machine having a water softening system, which does not require the use of any regenerating agents, such as salt.
According to this solution, the softening system uses special ionic exchange resins, of the thermally regenerable type; in this way, a regular topping up of a regenerating medium is no longer required, since the softening efficiency of the resins is restored when required, by flushing them through with hot water.
However, also the system described in U.S. Pat. No. 4,645,595 has some drawbacks. A first drawback is represented by the fact that the machine described in the above document, must provided for connection to a hot water supply network, i.e. a typical peculiarity of Anglo-Saxon markets (where washing machines are normally conceived for direct connection to two external water sources, i.e. hot and cold, respectively).
In this frame, therefore, the solution described in U.S. Pat. No. 4,645,595 does not appear appropriate for use in most European countries, where on the contrary washing machines are provided for connection to one cold water supply main only. On the other hand, the above document does not offer any indication concerning this specific aspect.
Anyway, a substantial problem of U.S. Pat. No. 4,645,595 is that also the softening system described therein is subject to periodical maintenance, i.e. the replacement of a cartridge containing the thermally regenerable resins, as they will loose their efficiency after a certain period of time. It is the aim of the present invention to solve the above problems.
Accordingly, the present invention has the aim to provide a household appliance utilizing water, such as a washing machine, which is equipped with a system for reducing the water hardness requiring no special regeneration agents for the materials used for water decalcification.
A further aim of the present invention is to provide a household appliance wherein the frequency of maintenance interventions and/or components replacement is minimized, which does not likely require periodic operations, such as the replacement of the above materials, at least for a period of time equal to the average useful life of a similar known household appliance.
In order to achieve such aims, it is the object of the present invention a household appliance utilizing water, in particular a washing machine, having a system for reducing the water hardness incorporating the features of the annexed claims, which form an integral part of the present description.